The present invention concerns an electric screwdriver used for screw tightening work, etc. in the assembling processes of automobiles and electronic equipment, more specifically an electric screwdriver capable of reducing the reactive force produced on the occasion of a screw tightening work, etc.
Conventionally, an electric screwdriver is generally used for screw tightening work, etc. in the assembling processes of automobiles and electronic equipment (see JP2001-62745A, for example).
By the way, this type of electric screwdriver is realized, generally, by interposing a clutch mechanism between the motor as driving source for rotation and the bit holder holding the screwdriving bit so that, in case a load with a torque no lower than prescribed level is applied to the bit holder during a screw tightening work, said clutch mechanism may work to shut off the transmission of motive power to the screwdriving bit, and by further comprising a tightening torque control means for shutting the power application to the motor, as required, to be capable of accurately controlling the tightening torque.
As described above, for the conventional electric screwdriver, various considerations were given in the matter of control of tightening torque, but no particular considerations were given, on the other hand, about the reactive force produced on the occasion of a screw tightening work. For that reason, there were such problems as fatigue of the worker holding the electric screwdriver with a long time of screw tightening work, because of the load applied on him, and drop of screw tightening accuracy due to changes in the holding state of the electric screwdriver by the worker, under the influences of reactive force, etc.